1. Field
The present invention generally relates to techniques for improving the performance of computer systems. More specifically, the present invention relates to a method and an apparatus for scheduling spin-up operations for a set of hard disk drives in a computer system.
2. Related Art
Some computer system manufacturers are beginning to offer high-storage capacity computer systems with hundreds or thousands of hard disk drives (HDDs). The power supply units (PSUs) in multi-HDD systems are typically provisioned to provide enough power to spin-up and operate all the HDDs in the system. However, since a typical HDD may draw more than twice as much current during spin-up as it draws during normal operation, manufacturers often provision PSU power capacities of more than 2 times of that needed for normal operating conditions so that most or all of the HDD can be spun-up at once.
This over-provisioning can be inefficient from cost and technology points of view, and results in wasted energy. Spin-ups are typically fairly rare events for highly utilized systems, so most of the operating life of over-specified power supplies may be spent operating at one-half or less of their maximum capacity. This can result in wasted energy since power supplies operate less efficiently when used far from their maximum capacity. Also, higher-power PSUs are typically more expensive, require more space, and add more weight to computer systems.
Hence, what is needed is a method and an apparatus for scheduling spin-up operations for a set of hard disk drives in a computer system in a manner that limits the aggregate system power required to perform the spin-up operations.